feat: RFCP MVP deployed on VPS

Iteration 1:
- Dark theme with 3-way toggle
- Dynamic heatmap gradient (blue→red)
- Radius up to 100km
- Save & Calculate workflow

Iteration 2:
- Terrain overlay toggle
- Batch height operations
- Zoom-dependent heatmap rendering

Infrastructure:
- Backend FastAPI on 8888
- Frontend static build via Caddy
- Systemd services
- Caddy reverse proxy integration

backend/venv/lib/python3.12/site-packages/anyio/abc/_resources.py

@@ -0,0 +1,33 @@
+from __future__ import annotations
+
+from abc import ABCMeta, abstractmethod
+from types import TracebackType
+from typing import TypeVar
+
+T = TypeVar("T")
+
+
+class AsyncResource(metaclass=ABCMeta):
+    """
+    Abstract base class for all closeable asynchronous resources.
+
+    Works as an asynchronous context manager which returns the instance itself on enter,
+    and calls :meth:`aclose` on exit.
+    """
+
+    __slots__ = ()
+
+    async def __aenter__(self: T) -> T:
+        return self
+
+    async def __aexit__(
+        self,
+        exc_type: type[BaseException] | None,
+        exc_val: BaseException | None,
+        exc_tb: TracebackType | None,
+    ) -> None:
+        await self.aclose()
+
+    @abstractmethod
+    async def aclose(self) -> None:
+        """Close the resource."""